In a variable volume air distributing unit, a bellows or bladder damper is inflated by the air being supplied to the unit. The pressure of the air supplied to the bellows is controlled by a pressure regulator of a type well known in the art. The bellows coacts with a cutoff plate to define a slot whose width varies with bellows inflation. In a typical air distributing unit the slot would be 36 inches long and vary in width from 0 inches (fully closed) to 0.75-1.0 inches (fully open). For proper control, it is necessary that the slot width be uniform for its entire length to minimize noise problems, to have a uniform air flow and the correct volumetric flow.
The bladder or bellows structure for air distributing units has been made in various configurations and constructions.
In one embodiment the bellows is self-contained and glued in place on the support structure. In another embodiment the bellows is a single sheet that is glued about its edges to the support structure to define therewith an air chamber for inflating/flexing the bellows. As noted above, there is a need to have a uniform slot width and, when the bellows is glued in place, this imposes rigid requirements in manufacturing because the gluing procedure dictates how much of the bellows is not glued and therefore, free to flex upon inflation and deflation of the bellows assembly. Additionally, the gluing procedure dictates how uniform the gluing is on individual units as well as between units. Because of possible variations in the gluing procedure, it is often necessary to individually calibrate the bellows damper of each air distributing unit after they are installed.